Part one: In Montana, Native Americans fear a leak could destroy their way of life, but local politicians worry about the threat of protesters above all else

“)ur people call it the black snake because it is evil,” says Tressa Welch, as thunder clouds steamroll the blue sky over the plains of Wolf Point. “And like snakes they come out of nowhere, they slither and strike unknown.”

She faces southwards where, a couple of miles away, forks of lightning crack over the Missouri River. The 2m acre Fort Peck Indian Reservation straddles this winding water source, providing sustenance for the almost 7,000 Assiniboine and Sioux tribe here and thousands of others throughout north-east Montana. It is the river that Welch and other Native American activists on the reserve say the Keystone XL oil pipeline – or the “black snake” – will corrupt.

The river maintains the deer, the fish, the native plants, sweet grasses and sacred sage. “Anything that threatens my way of life and my spiritual well-being, I consider myself at war with,” she says, her two-year-old daughter by her side. “I will do whatever it takes.”

Although the XL is expected to cross the Missouri just outside of the reservation, it will do so about 40 miles upstream of the tribes’ multimillion-dollar water treatment plant, which supplies clean water to communities throughout the entire region. A leak at this junction, they say, could be catastrophic. The project’s backers insist it will be safe.

The gargantuan underground pipeline is set to carry a daily load of 830,000 barrels of oil over 1,204 miles, from the Athabasca oil sands in Alberta, Canada – where it enjoys the support of the prime minister, Justin Trudeau – across the US border into eastern Montana. It will travel down to South Dakota, eventually linking with the first Keystone pipeline, which was completed in 2010, in southern Nebraska. The route connects not just countries and states, but three US presidencies. First proposed by the private Canadian infrastructure giant TransCanada during George W Bush’s final months in office, the project was eventually rejected by the Obama administration in 2015, only to be resurrected almost as soon Donald Trump was sworn in at the beginning of this year…